1. FIELD OF THE INVENTION
The present invention relates to a molded amide resin product and a method for its preparation. Particularly, it relates to a molded product by reaction injection of an amide resin and a method for its preparation. More particularly, it relates to a molded product having excellent mechanical properties at room temperature and low temperatures, little dimensional change and little deterioration in the rigidity due to absorption of water, and an excellent outer appearance, and a method for its preparation.
2. DISCUSSION OF BACKGROUND
In recent years, a so-called reaction injection molding (hereinafter referred to simply as "RIM") has been proposed as a method for obtaining a molded product, wherein a highly reactive liquid material is injected into a mold, followed by the polymerization reaction of the liquid material, and RIM is expected to be a highly prospective technique.
The RIM technique was practically developed in the field for the production of molded products from polyurethanes. Recently however, the same technique has been applied also to base materials such as amide resins, unsaturated polyester resins or epoxy resins. Among them, amide resins are expected to be particularly useful for RIM since they have merits such that they are excellent in toughness, heat resistance, electrical properties, friction resistance and abrasion resistance, they are moldable under low injection pressure since the flowability of the starting material composition is good, they are moldable into any desired shapes ranging from thin molded products to thick molded products, the transferability of the mold surface is good, and the polymerization reaction can be easily accomplished since heat generation during the polymerization is little.
However, the amide resins are inadequate in the impact resistance at low temperatures. Further, since they have high water absorptivity, the deterioration in the rigidity and the dimensional change of the molded product are substantial. Further, they have a drawback that the heat resistance is inadequate for baking finish. It has been proposed to incorporate a certain block copolymer to the amide resin to overcome such drawbacks (Japanese Examined Patent Publication No. 40120/1979). According to this proposal, however, the deterioration in the rigidity is substantial although the impact resistance at low temperatures is improved. As another method for overcoming the above drawbacks, it has been proposed to add a filler to the amide resin. However, the impact resistance at a low temperature will not be improved by this method, although the deterioration in the rigidity and the dimensional change of the molded product due to water absorption will be reduced and the heat resistance can be improved.
As still another method for overcoming the above drawbacks, it has been proposed to add an aromatic polyamide to the amide resin. However, this method has a drawback that the molded product tends to have poor impact resistance although it is possible to suppress the water absorptivity by this method.